This invention relates to the chemical conversion of dicarboxylic acid, anhydride, or half acid groups into cyclic imide groups by the reaction of aqueous ammonia or an aqueous amine solution on copolymers containing the reactive groups.
A wide variety of imide copolymers should be preparable, with modified properties and functionalities, depending on the amine utilized. By varying the substituent on the imide nitrogen, copolymers with markedly improved properties, such as heat distortion temperature, solvent resistance, flexibility, and flow characteristics may be prepared.
Thus, the imide or N-phenylimide copolymers have higher glass transition temperatures than the corresponding dicarboxylic acid or anhydride containing copolymers, the glass temperature increasing with increasing imide content. This enhanced glass temperature is a very useful and desirable property for thermoplastic polymers.
Copolymers with imides of ethylenically unsaturated dicarboxylic acids, such as maleimide, can be prepared by direct copolymerization of the monomers. However, the imides are expensive and relatively unavailable. Although, the preparation of these copolymers by direct polymerization usually yields the 1:1 alternating copolymer, special techniques have been developed to prepare non-equimolar copolymers. Methods have been developed to convert anhydride containing copolymers to the corresponding imide copolymers by reacting the copolymers with anhydrous ammonia or with anhydrous amines in organic solvents. However, these methods involve the necessity of either handling anhydrous gases or using the two step process of preparing a solid half acid amide salt with subsequent cyclization of the salt to the desired imide product.